Size press

Abstract: The invention concerns a size press, comprising a first roll (12), which is mounted rigidly on the frame (11) of the size press, as well as a second roll (16), which forms a size-press nip (N) with the first roll and which is mounted, at a level higher than the level of said first roll (12), on a loading arm (19) that is supported pivotally on a transverse shaft (20) on the frame (11) of the size press. The loading arm (19) can be pivoted by means of loading cylinders (22) so as to produce the desired pressure level in the nip (N) and to open said nip for threading of the web (W) and for replacement of rolls. The paper web (W) is passed into the nip (N) as guided by a guide roll (23) and out of the nip (N) over a spreader roll (25) or an air-turning device. The rolls (12) that form the size-press nip (N) have been arranged in such a way in relation to one another that the nip plane passing through the rolls forms an angle of 35...120°, advantageously 50...60°, preferably 55°, in relation to the horizontal plane. The web (W) has been arranged to be passed into the nip (N) at an angle of substantially 90° in relation to the nip plane and to be passed out of the nip (N) at an angle of 90° ± 7° in relation to the nip plane.

Description: The invention concerns a size press, comprising a first roll, which is mounted rigidly on the frame of the size press, as well as a second roll, which forms a size-press nip with the first roll and which is mounted, at a level higher than the level of said first roll, on a loading arm that is supported pivotally on a transverse shaft on the frame of the size press, said rolls that form the size-press nip being provided with coating devices of the Short Dwell type for spreading of films of coating agent onto the faces of said rolls, the coating agent being arranged to adhere, in the nip, from said roll faces onto the paper web or equivalent that passes through the nip, said loading arm being pivotal by means of loading cylinders so as to produce the desired pressure level in the nip and to open said nip for threading of the web and for replacement of rolls, and the paper web or equivalent being passed into the nip as guided by a guide roll and out of the nip over a spreader roll or an air-turning device. The most important objective of surface sizing of paper is, in view of improving the printing qualities of the paper, to increase the bonds between the fibres by using binding agents soluble in water, most commonly starch. The surface-treatment device most commonly used in surface sizing is a size press. The size press comprises size-press rolls, which are mounted in the conventional way on the frame of the press and which form a nip with one another, the paper web being passed through said nip. It is a conventional mode of adding size to the paper face that a size pond is arranged in the gap placed before the nip formed by the roll, the paper web running through said pond. The web is introduced into the nip as guided by a guide roll, so that the web is guided into the nip as precisely in the direction of the tangent of each press roll as possible. A further development of the size presses that make use of the size-pond principle consists of film-size presses, in which each roll in the size press is provided with a coating device, e.g. as described in DE-C-427 531 or preferably of the Short Dwell type, which devices spread and smooth the size films or equivalent onto the roll faces, said films being then transferred to the paper web to be treated in the roll nip. Besides for surface sizing, such film-size presses may also be used for pigmenting of paper. It is quite a conventional construction in size presses that the lower one of the size-press rolls is mounted on the size-press frame stationarily, whereas the other one, i.e. the upper size-press roll, is mounted on a particular loading arm, which is again linked pivotally on the frame of the size press. Between the size-press frame and the loading arm, loading cylinders are fitted, by whose means the desired nip pressure can be produced in the size-press nip and by means of which cylinders the nip can be opened for tail threading of the web and further for replacement of roll. In the size presses operating with the size-pond principle, the size-press rolls were usually arranged so that the plane that passes through the axes of the rolls, i.e. the nip plane, is substantially horizontal or just very slightly inclined from the horizontal plane. This is also understandable, because by means of such an arrangement it was possible to form a suitable size pond in the gap placed before the roll nip. The film size presses that have been developed further from these size presses operating with the size-pond principle and in which the size-press rolls are provided with particular coating devices, have substantially equal basic constructions in the conventional technology. Thus, also in these prior-art film-size presses, the size-press rolls have been arranged so that the angle between the rolls, i.e. the angle of the nip plane in relation to the horizontal plane, is very little, as a rule of an order of 15...30°. One such solution is described, e.g., in the applicant's FI-A-87,475 of earlier date. In the solution in accordance with said patent, the paper guide roll over which the web is passed into the nip is arranged above the lower size-press roll, being attached to a pivot arm, which is linked pivotally on the frame of the size press by means of a transverse pivot shaft so that, for replacement of roll, the paper guide roll can be pivoted into a position that has been shifted aside from the running position. One drawback of such a solution is complicated construction, and, as a result of that, high cost. Ordinarily, the paper guide roll has, however, been attached to a frame of its own, which has been separate from the frame of the size-press rolls. Owing to the relative location of the size-press rolls, it has been necessary to construct the frame of the paper guide roll quite massive, because it has been necessary to support the paper guide roll above the size press. It has been necessary to do this in order that it should be possible to make the web pass into the nip as precisely parallel to the tangent of each press roll as possible. In such a solution, it has not been possible to attach the paper guide roll to its frame directly, but, as a rule, it has been attached by means of an articulated pivot arm linked to the frame construction in order that it should be possible to lift said guide roll out of the way in connection with replacement of press rolls. Thus, in such solutions, it has been a problem that they have required a considerable amount of space both in the machine direction and in the vertical direction in view of pivoting of the guide roll. During pivoting or lifting of the guide roll, the paper guide roll and its pivot arm must rise to a very high level, which was, in prior art, a factor determining the height of the paper mill hall. Owing to the fact that the angle of the nip plane of the size-press rolls in relation to the horizontal plane has been very little, i.e. of an order of 15...30°, it has been necessary to pass the web out of the nip so that the web has followed the face of the upper roll over some distance. This has again resulted in the significant drawback that the web is separated from the roll indefinitely, and often in so-called "web-stealing", i.e. a tendency of the web to follow the lower roll. This has produced a fluttering movement in the web as the web is alternatingly separated from, and adhering to, the roll. This has again had the consequence, especially in pigmenting, that the quality of the coating applied to the web has deteriorated, and a fully even coating has not been produced. In view of improving the web separation properties, in some cases, air-blow boxes have been used underneath the size press rolls, attempts having been made to separate the web from the faces of the size-press rolls by means of the air jets coming out of said boxes. Since the air-blow boxes are placed underneath the size-press rolls, contamination of the air-blow boxes has, however, constituted quite an important drawback. The same also applies to the web guide roll placed underneath the nip. In particular in the case of pigmenting, out of reasons of quality, it would be optimal if the web could be taken out of the nip at an angle of 90° in relation to the nip plane. In such a case, the quality of the coating would become as good as possible. Further, it has been a drawback in the prior-art solutions that the size-press rolls have been of different hardness, i.e. the lower size-press roll and the upper size-press roll have been provided with coatings of different hardness. This has come exactly from the very fact that, after the nip, the web has initially followed the upper roll and, nevertheless, attempted to adhere to the lower roll. In the prior art, as a rule, the upper size-press roll has been harder than the lower roll. Thus, for the size press, it has been necessary to keep spare rolls of two types on stock. This has constituted quite an important cost factor, and in some cases also a problem of space. The object of the present invention is to provide a size press by whose means the drawbacks involved in the prior-art constructions are avoided and by whose means, further, the coating result can be improved over the prior-art solutions. In view of achieving the objectives of the invention, the invention as described in claim 1, is mainly characterized in that the rolls that form the size-press nip have been arranged in such a way in relation to one another that the nip plane passing through the rolls forms an angle of 35...120°, preferably 50...60°, in relation to the horizontal plane, and that the web has been arranged to be passed into the nip at an angle of substantially 90° in relation to the nip plane and to be passed out of the nip at an angle of substantially 90° in relation to the nip plane. By means of the invention, compared with the prior-art solutions, a number of advantages are obtained, of which, e.g., the following should be mentioned in this connection. By means of the invention, the running line of the web can be made very smooth, which results in easy tail threading and good runnability of the web. The web can be separated from the nip at an angle of 90° without any extra support members, such as air-blow boxes or equivalent. In connection with the invention, it is, however, possible to use such support members if they are considered necessary. As the web is taken out of the web substantially at an angle of 90°, the quality of the coating can be made very good. In a size press in accordance with the invention, it is possible to use rolls of equal hardness, unlike the prior-art solutions, in which one-sided separation of the web requires rolls of different hardness. Thus, for the size press, a lower number of spare rolls are needed than in the prior art. The invention permits the paper guide roll that precedes the nip to be mounted on a separate, stationary frame so that it does, however, not hamper the replacement of the nip rolls in any way. In the embodiment of the solution in accordance with the invention in which the nip has been constructed to be opened in two stages so that the first open position is a normal tail threading position, whereas the second open position is a roll replacement position, the lower nip roll can be replaced even if the upper roll is in its position. It is a further remarkable advantage of the invention that it has been possible to minimize the entire space that is required by the size press in the longitudinal direction of the machine, i.e. in the machine direction. The further advantages and characteristic features of the invention will come out from the following detailed description of the invention. In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic side view of a size press in accordance with the invention. Figure 2 is a schematic sectional view of a coating device of the Short Dwell type used in a size press in accordance with the invention. Figure 3 is a schematic illustration of the running of the web line in a size press in accordance with the invention. Figure 4 is an illustration corresponding to Fig. 1 of a size press in which contact-free dryers have been fitted in the path of the web coming out of the dryer before the drying cylinder. Figure 5 is a schematic illustration of a solution in which the turning, spreading, and guiding of the web after the nip are arranged by means of air-turning devices. In Fig. 1, the size press is denoted generally with the reference numeral 10. The size press 10 comprises a size-press frame 11, which is mounted on a base B and on which the size-press rolls 12,16 are mounted in the conventional way. The bearing housing 13 of the first size-press roll 12, i.e. of the lower roll, is mounted directly on the frame 11 of the size press and attached to it rigidly. On the other hand, the bearing housing 17 of the second size-press roll, i.e. of the upper roll, is mounted on a loading arm 19, which is linked pivotally to the size-press frame 11 by means of a pivot shaft 20 transverse to the machine direction. Between the loading arm 19 and the size-press frame 11, loading cylinders 22 are fitted, by whose means the loading arm 19 is loaded so as to produce a nip pressure of the desired magnitude in the nip N formed by the lower roll 12 and the upper roll 16. Either one of the size-press rolls 12,16, preferably the upper roll 16, or alternatively both of the size press rolls 12,16, may be variable-crown rolls in order that the nip N pressure could be brought to the desired level in the transverse direction of the machine. Each size-press roll 12,16 is provided with a coating device 15,21 of the Short Dwell type, by whose means the size films or equivalent coating-agent films are applied and smoothed onto the faces 14,18 of said rolls. When the web W runs through the nip N, the films of coating agent are transferred from the roll 12,16 faces 14,18 to the web W'. The web W is passed into the size-press nip N over the guide roll 23, which is mounted on a stationary frame 24 which has been installed on the base B. After the size-press nip N, the web W' is passed over the spreader roll 25 further to the dryer section, whose first drying cylinder is denoted with the reference numeral 26. The construction and the operation of the coating devices 15,21 of the Short Dwell type are described in more detail in the description related to Fig. 2. The means of support of the spreader roll 25 are not described in more detail in this connection. Fig. 2 is a more detailed schematic sectional view of the construction of a coating device of the Short Dwell type used in a size press in accordance with the invention. Fig. 2 specifically shows the coating device 15 of the Short Dwell type placed in connection with the first size-press roll 12 in the size press 10, but it is fully obvious that the coating device 21 placed in connection with the second size-press roll 16 may have a construction of a corresponding type. In the coating device 15 in accordance with the invention, as is also the case in coating devices of the Short Dwell type in general, the application of the coating-agent film onto the face 14 of the roll 12 is carried out so that, in the coating device 15, the coating agent is supplied under pressure into the coating-agent chamber 153, which is defined by the coating member 151, by the front edge 152 of the coating-agent chamber 153, by the face 14 of the size-press roll, and by lateral seals (not shown). The front edge 152 of the pressurized coating-agent chamber 153 may be similar to that shown in Fig. 2, so that said front edge 152 rests against the roll face 14, or there may be a gap between the front edge 152 of the coating-agent chamber and the roll face 14, through which gap the overflow of the coating agent is arranged from the coating-agent chamber 153 into the collecting basin. In the embodiment shown in Fig. 2, the coating member that is used is a coating bar 151, which is mounted rotatably in a bar cradle 154, which is made of, e.g., polyurethane or of an equivalent material. The bar cradle 154 is mounted in its holder 155, in which it is secured in its position by means of a fastening device 156. Behind the bar cradle 154 of the coating member, a profile rib 158 is fitted, which rests against the rear face of the bar cradle 154 by the intermediate of a loading hose 157. To the frame of the coating device 15, adjusting spindles 159 have been fixed by means of suitable fixing means (not shown), a number of such spindles being fitted as uniformly spaced in the transverse direction of the machine. For each adjusting spindle 159, on the frame of the coating device 15, preferably spindle motors (not shown) are mounted, by whose means, by displacing the adjusting spindles 159, the profile bar 158 is pulled and/or pushed so that the profile bar 158 can be deflected in the desired way. The coating device 15 as shown in Fig. 2 is provided with a coating-agent supply pipe 161 transverse to the machine direction, into which pipe the coating agent is supplied from one end or, preferably, from both ends of said supply pipe 161. The supply pipe 161 is provided with a great number of holes or equivalent nozzles 162 in the transverse direction of the machine, said holes or nozzles forming a throttle for the flow of the coating agent. Thus, the coating agent is passed out of the supply pipe 161 through the nozzles 162 into the coating-agent chamber 153. The front edge 152 of the coating-agent chamber 153 is installed in its holder 160 in the normal way. The construction shown in Fig. 2 is just one example of a coating device 15 of the Short Dwell type used in a size press 10 in accordance with the invention. Other constructions of the coating device may show even considerable variation within the scope of the invention, but it is an essential feature of the coating devices 15 of the Short Dwell type that the device comprises a pressurized coating-agent chamber 153, which is defined by the coating member 151, by the front edge 152 of the coating-agent chamber, by the roll face 14, and by lateral seals (not shown). In the following, in addition to Figs. 1 and 2, reference is also made to Fig. 3. As can be seen from Fig. 1 and especially from Fig. 3, the size-press rolls 12,16 are mounted in the size press in a way different from the conventional arrangement, so that the angle α of the nip plane T-T, which runs through the central axes of the size-press rolls 12,16, in relation to the horizontal plane S is substantially larger than in the prior-art solutions. In the invention, said angle α is 35...120°, advantageously 50...60°, preferably 55°. The web W is passed into the nip N as guided by the guide roll 23, so that the web W is guided into the nip N as precisely parallel to the tangent of each press roll 12,16 as possible. Thus, this means that the web W is passed into the nip N substantially at an angle of 90° in relation to the nip plane T-T. The inlet angle of the web running line in relation to the nip plane is, in Fig. 3, denoted with the reference denotation β 1 . The coated web W' is passed, in the embodiment of Fig. 3, from the nip N over the spreader roll 25 to further processing, as was already stated above. As was already stated in the description above, especially in pigmenting, it is preferable to pass the coated web W' out of the nip N as precisely as possible at an angle of 90° in relation to the nip plane T-T. As can be seen clearly from the figures in the drawing, in the invention this objective has been achieved so that the coated web W' can be passed out of the nip N at an angle β 2 , which is 90 ± 7°. The variation in the outlet angle β 2 of the web line has been produced thereby that the position of the spreader roll 25 is adjustable in the vertical direction. This adjustability can be arranged in a simple way by conventional means. Thus, by means of the adjustability of the position of the spreader roll 25, it is possible to regulate the outlet angle β 2 of the web line in relation to the nip plane T-T in the desired way. Such a need of adjustment may arise, for example, when the properties of the upper face and the lower face of the web W to be coated differ from one another, e.g., in respect of porosity or smoothness. Such properties of the web W affect the adhesion between the web W and the roll 12,16 faces 14,18. The size press 10 shown in Fig. 4 is similar to that already described in connection with Fig. 1. The embodiment shown in Fig. 4 differs from that shown in Fig. 1 so that the web W' is passed from the size-press nip N onto the first drying cylinder 26 in the dryer section so that the web W' is dried, after the spreader roll 35 by means of contact-free dryers 36,37 before the web W' is passed onto the drying cylinder 26. Such contact-free dryers suitable for the purpose are, for example, convection dryers, infrared dryers and/or air dryers, such as hot-air blow dryers. Such contact-free web W' dryers 36,37 are advantageous and necessary especially when large coating quantities are run into the web W' by means of the size press 10. In Fig. 4, it is shown further that, in the guiding of the web W' onto the drying cylinder 26, additionally, air blowing by means of an air-turning device or an equivalent blow box 38 is used as an aid. The embodiment shown in Fig. 5 differs from that shown in Fig. 4 in the respect that, in the embodiment of Fig. 5, the spreader roll 35 as shown in Fig. 4 has been completely substituted for by air-turning devices 38a,38b, by whose means the web W' is turned and guided onto the first drying cylinder 26 in the dryer section. In the embodiment of Fig. 5, it is shown further that air blows coming out of blow boxes 38c,38d or out of equivalent air-turning devices have been arranged to support the web W'. In the embodiment of Fig. 5, it is also possible to use contact-free web W' dryers similar to those described in relation to Fig. 4. In a size press 10 constructed in the way described above, rolls of equal hardness can be used as the upper and lower rolls 12,16. Thus, the rolls 12,16 can be provided with identical coatings, in which case an equally high number of spare rolls are not needed as were needed in the prior art. Replacement of the rolls 12,16 can also be carried out in a simple way in a size press 10 in accordance with the invention. As can be seen in particular from Figs. 1, 4 and 5, by pivoting the loading arm 19, the rolls 12,16 can be brought into such a roll replacement position in which the lower roll 12 can also be replaced readily even if the upper roll 16 were in its position. The nip N is preferably constructed so that it is opened in two stages, so that, by means of the loading arm 19 and the loading cylinders 22, the upper roll 16 can be pivoted first into a normal tail threading position, in which the tail threading of the web W can be carried out very easily and simply because of the substantially straight web line. After the catches of the tail threading position (not shown) have been opened, the nip N can be opened to the roll replacement position.

Claims: Size press, comprising a first roll (12), which is mounted rigidly on the frame (11) of the size press, as well as a second roll (16), which forms a size-press nip (N) with the first roll and which is mounted, at a level higher than the level of said first roll (12), on a loading arm (19) that is supported pivotally on a transverse shaft (20) on the frame (11) of the size press, said rolls (12, 16) that form the size-press nip (N) being provided with coating devices (15, 21) of the Short Dwell type for spreading of films of coating agent onto the faces of said rolls (14, 18) and transfer of said coating agent from said roll faces onto the paper web (W) or equivalent that passes through the nip, said loading arm (19) being pivotal by means of loading cylinders (22) so as to produce the desired pressure level in the nip (N) and to open said nip for threading of the web (W) and for replacement of rolls, and the paper web (W) or equivalent being passed into the nip (N) as guided by a guide roll (23) and out of the nip (N) over a spreader roll (25, 35) or an air-turning device (38, 38a, 38b, 38c, 38d), characterized in that the rolls (12, 16) that form the size-press nip (N) have been arranged in such a way in relation to one another that the nip plane (T-T) passing through the rolls forms an angle (α) of 35...120°, preferably 50...60°, in relation to the horizontal plane (S), and that the guide roll (23) and the spreader roll (25, 35) or the air-turning device (38, 38a, 38b, 38c, 38d) have been arranged so that the web (W) is to be passed into the nip (N) at an angle (β 1 ) of substantially 90° in relation to the nip plane (T-T) and to be passed out of the nip (N) at an outlet angle (β 2 ) adjustable at both sides of 90° in relation to the nip plane (T-T). Size press as claimed in claim 1, characterized in that the allowance for adjustment of said outlet angle (β 2 ) of the web line is ± 7°. Size press as claimed in any of the preceding claims, characterized in that, in view of adjusting the outlet angle (β 2 ) of the web line, the spreader roll (25,35) or the air-turning device (38a) has been arranged so that it can be adjusted in the vertical direction. Size press as claimed in any of the preceding claims, characterized in that, in the path of the web (W') that comes out from the size-press nip (N), after the Spreader roll (25,35) or the air-turning device (38a,38b), before the first drying cylinder (26) in the dryer section, contact-free web (W') dryers (36,37) are fitted, such as convection dryers, infrared dryers, or hot-air blow dryers. Size press as claimed in any of the preceding claims, characterized in that the angle (α) of the nip plane (T-T) in relation to the horizontal plane (S) is 55°. Size press as claimed in any of the preceding claims, characterized in that the guide roll (23), over which the web (W) is passed into the nip (N), has been mounted stationarily on a frame (24) separate from the size-press frame (11). Size press as claimed in any of the preceding claims, characterized in that the rolls (12,16) that form the size-press nip (N) are provided with a coating, which is of substantially equal hardness on both rolls.

Inventors: KORHONEN VILLE, LAITINEN PEKKA, KORHONEN, VILLE, LAITINEN, PEKKA
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21H23
IPC codes: D21H23